Hydropneumatic counterbalance



Feb. 25, 1941., R. G. DE LA MATER N 2233245 HYDRO'PNEUMATIC COUNTERBALANCE Original Filed Aug. 3, 1937 I2 Sheets-Sheet l 'Q I P 613544474757? s l\ V wig .MMM

Feb. 25, 1941. R. 6. DE LA MATER 2,233,245

HYDRO'PNEUMAT I C COUNTERBALANCE Original Filed Aug. 3, 1937 2 Sheets-Sheet 2 w, \amsm up stroke of the pump rods.

Patented Feb. 25, 1941 UNITED STATES PATENT OFFICE HYDROPNEUMATI C CO UN TE RBALANCE West Virginia Application August 3, 1937, Serial No. 157,189

Renewed August 2, 1939 55 Claims.

This invention relates to counterbalances and more particularly to hydropneumatic counterbalances especially adapted for use with oil well pumping rigs.

As is well known, it is the common practice to counterbalance the walking beams of oil well pumping rigs to equalize the power demand throughout the pumping cycle. On the down stroke of the rods and pump plunger, the weight suspended from the well end of the walking beam i essentially the weight of the pump rods. On an uncounterbalanced rig, this weight would pull the beam down and no power would be required for moving the beam. On the upstroke, the weight suspended from the nose end of the walking beam is essentially the weight of the rods plus the weight of the fluid being lifted. On an uncounterbalanced rig the prime mover is required to furnish the power to lift this total weight. As a result, it will be obvious that the power cycle would be very uneven on an uncounterbalanced rig,the power varying from negative to positive and being greatly affected by other forces such as inertia, etc. I

In counterbalancing an oil pumping rig, it is the common practice to provide counterbalancing approximately to the extent of the weight of the pump rods plus half the weight of the fluid that is lifted on the up stroke of the pump rods. Thus on the down stroke, the weight of the counterbalance is partially balanced off by the weight of the rods and the remaining unbalanced weight of thecounterbalance is equal to half the weight of the fluid to be lifted on the On the up stroke, the counterbalance, which was raised during the down stroke, balances off the weight of the pump rods plus half the weight of the fluid, and accordingly the Weight required to be lifted by the prime mover is half the weight of the fluid.

Thus, with a conventional counterbalanced pumping rig, the prime mover is loaded the same on both strokes, the load on the up stroke being half the weight of the fluid and the load on the down stroke being a portion of the weight of the counterweights equal to half the weight of the fluid lifted on each up stroke. The counterbalancing is usually provided in either of two ways, namely, by counterweighting the walking beam itself or by counterweighting the crank shaft from which thepitman is driven,

Each of these systems possesses advantages which are offset by substantial disadvantages. For example, the counterweighting of the walking beam has the advantage of applying the counterbalance as close as possible to the application of loads to the walking beam, which position is the ideal position for counterbalancing. This arrangement, however, is disadvantageous because of the great amount of weight which must be mounted on the beam. For example, the pump rods of a 6,000 ft. well weigh approximately 11,000lbs. and the fluid lifted on each up stroke of the pump rods may weigh as much as 6,000 lbs. Under such conditions, the walking beam will be conventionally counterweighted to the extent of 14,000 lbs, namely, 11,000 lbs (the weight of the pump rods) plus 3,000 lbs. (half the weight of the fluid being lifted). Obviously the inertia of these weights at the top and bottom of the pumping stroke is great and the beam must be of substantial construction to support the loads to which it is subjected.

In case of a pitman failure the weight on the Walking beam obviously will pull the beam downwardly, and unless stopped by a conventional headache post, may wreck the entire pumping rig. A further disadvantage in coun terweighting the walking beam lies in the difficulty in handling and adjusting the counterbalance weights. Such weights do not adapt themselves to ready adjustment when changes occur in pumping conditions, it frequently being necessary to bring a hoist to the rigto remove or add weights.

Rotary crank weights have been more extensively used Without beam weights because of certain inherent advantages which they possess. For example, in case of a failure of the pitman or pump rods materially less damage results than if the weights were carried by the walking beam. Moreover, it is more convenient to handle the beam when the beam and pitman are disconnected. Rotary crank weights are fairly readily adjustable for lag or lead, and they have the advantage of always maintaining the pitman in tension instead of alternately in tension and under compression. While rotary crank weights are more readily adjustable than beamweights, they are far from easily adjustable and present substantial difliculties in handling and adjusting. Moreover, they obviously add substantially to the loads on the crank and crank shaft.

In recent years it has been proposed to counterbalance the walking beam of a well rig by pneumatic means which operates to store energy on the down stroke of the pump rods and to expend energy on theiup stroke. Such a mechanism involve numerous advantages over conventional counterweigh-ting in that it permits the application of the counterbalancing force substantially at the ideal point, and eliminates the use of heavy masses of reciprocating or rotating counterweights. Thus the pumping equipment is more portable, easier to install, and requires much less foundation for stability. However, a pneumatic counterbalance involves numerous disadvantages and leaves much to be desired in an apparatus of this character.

For example, a pumper will frequently have in his charge as many as forty pumping wells scattered over a considerable territory and accordingly he may be able to visit each well only once every eight or twelve hours. Many wells are pumped night and day and during the night may not be properly inspected due to inadequate light facilities, etc. Accordingly it is essential that a counterbalance unit be made as trouble free as possible, and pneumatic counterbalances fail to meet this requirement because of numerous possibilities of failure which are always present. Some minor part failing to function properly may cause considerable damage or even cause a complete wreck before the pumper discovers the trouble or even gets around to the well for inspection. For example, the failure of the air compressor on a pneumatic type of counterbalance may result in the complete unbalancing of the unit. The springing of a leak in the packing of the compressor or the packing of the counterbalance piston, if this leak should be of greater capacity than the air compressor will have the same result. It also will be apparent that the failure of the lubricator in the cylinder of a pneumatic counterbalance or the loss of level of oil in the lubricator will have serious results.

It is possible that a pumping rig may be shut down for hours and even days, and during such period it is essential that there be no material loss of pressure dueto leakage, and such loss of pressure'cannot be effectively prevented in a pneumatic counterbalance. In such a counterbalance, air is confined at a minimum pressure of approximately 200 lbs. per square inch and such pressure increases to as high as 400 lbs. pressure per square inch. A single stage compressor for supplying and maintaining pressure in a counterbalance of thistype must have a relatively long stroke since the air must be compressed to from one-eighth to one-fourteenth of its volume before raising the pressure sufficiently to discharge it into the counterbalance cylinder.

In effecting any appreciable increase in the operating pressure of a pneumatic counterbalance a substantial amount of air must be introduced into the system, and the air compressor will become quite hotunless auxiliary means are provided to cool it. Moreover, the compressor of a pneumatic counterbalance is in continuous operation drawing air from the atmosphere and discharging it into the system, the air being released from the system at a maximum predetermined pressure. Consequently, since the air in an oil field is frequently contaminated with dust or corrosive gases, considerable damage may be done to working parts of the counterbalance. It will be appreciated that this presents a serious problem when air is being continuously introduced into the system through the compressor, valves, etc., such air, ofcourse, coming into constant contact withother working parts of the systemsuch as the piston and cylinder.

Fromthe foregoingit will be apparent that the provision of an eflicient, practicable and trouble proof counterbalance for oil well pumping rigs presents very serious problems, and it is the principal objects of the present invention to provide a counterbalance which possesses all of the advantages of prior mechanisms while substantially completely eliminating the disadvantages thereof, the apparatus being capable of operating over long periods of time without attention and with substantially no chance of failure.

More specifically, an important object of the invention is to provide a hydro-pneumatic counterbalance wherein all of the advantages of a pneumatic counterbalance are retained while eliminating the disadvantages thereof such as the necessity for the constant pumping of air, the necessity for cooling the compressor, the necessity for continuously introducing new and contaminated air into the system, the necessity for paying close attention to the lubricating system, etc.

A further object is to provide a hydro-pneumatic counterbalance wherein each down stroke of the plunger compresses and accordingly stores energy in a body of a compressible fluid such as air, but wherein a body of a non-compressible fluid such as oil is interposed between the compressible fluid and the piston and cylinder to positively prevent the leakage of air around the plunger, the pressure in the system being maintained and regulated by the introduction of noncompressible fluid into the system, the rate of pumping of the non-compressible liquid being very small and capable of accomplishment with a small simple pump.

A further object is to provide a hydro-pneumatic counterbalance having two relatively movable parts one comprising a plunger and the other comprising a cylinder and receiver, the two parts being respectively connected to a stationary support and to the walking beam adjacent the well end thereof and to provide means operable by the horizontal component of movement of the receiver, during oscillation of the walking beam, to maintain or increase the pressure of the receiver by introducing non-compressible fluid thereinto.

A further object is to provide a hydro-pneu-. matic counterbalance wherein the compressible fluid is confined against leakage instead of being released when it exceeds a predetermined pressure, and to provide a pump for supplying noncompressible fluid to the receiver with a blow off valve between the pump and the receiver to determine the pressure at which non-compressible fluid will be introduced into the receiver and to determine the maximum pressure in the receiver, thus providing perfect controlling of the counterbalancing action.

A further object is to provide an apparatus of the character referred to wherein relative minimum and maximum pressures within the receiver may be varied by varying the relative volumes of compressible and non-compressible fluids, thus varying the counterbalancing action.

A further object is to provide novel means for supplying the initial charge of compressible fluid to the receiver to build up the desired pressure therein. Y

A further object is to provide means for utilizing reciprocating movement of the counterbalance plunger for supplying the initial charge of air to the receiver.

A further object is to provide a clearance space communicating with the upper end of the cylinder portion 2| fitting within the flange I9.

above the top of the plunger in the upper limit of movement thereof to limit the pressure generated by the plunger when the latter is utilized for supplying the initial charge of air to the receiver. 7 A further object is to provide a system for the non-compressible fluid whereby any such fluid leaking past the piston may be returned to a reservoir, and wherein such reservoir supplies non-compressible fluid to the pump to be supplied to the receiver.

ther objects and advantages of the invention will become apparent during the course of the following description.

In the drawings I have shown one embodiment of the invention. In this showing- Figure 1 is a side elevation of a standard well rig showing the principal parts of the invention applied thereto, the piping connections, etc., being eliminated for the purpose of simplicity,

Figure 2 is a schematicside elevation of the counterbalance system as a whole, parts being broken away and parts being shown in section, and,

Figure 3 is a fragmentary sectional view of a slightly modified type of plunger.

Referring to Figure 1, the numeral designates a conventional walking beam mounted as at 2 for oscillation on the upper end of a conventional sampson post 3. The walking beam is oscillated 1 in the usual manner by a pitman 4 driven by a crank 5 operated by the usual prime mover (not shown). The well end of the beam is connected by the usual polished rod carrier 6 to the usual pump or polished rods I. A conventional apparatus of this character is provided with headache posts to prevent damage to the apparatus and injury to workmen in the event of breakage of any part of the apparatus. It will become apparent, however, that the present invention functions to permit the elimination of the usual headache posts by limiting the swinging movement of the walking beam I.

While the present invention has been illustrated as applied to a conventional type of pumping rig, it will be apparent that it is capable of application to any analogous structure.

The present invention comprises a counterbalance unit indicated as a whole by the numeral It. This unit comprises a receiver having upper and lower heads I2 and I3 preferably welded in position as indicated in Figure 2. A supporting member I4 is welded to the lower head i3 and is pivoted as at I5 to a suitable support l6 shown in Figure 1 as being mounted upon the foundation H. The head I2 is provided with an axial opening l8 surrounded by a relatively heavy flange l9 welded in position on the head |2. While the receiver II has been shown as an integral part of the counterbalance unit, it will become apparent that this arrangement is preferred but not essential.

A cylinder 23 projects downwardly through the opening |8 into the receiver and is provided adjacent its upper end with an annular enlarged Such portion of the cylinder is provided with an outstanding annular flange 22 bolted to the flange [9 as at 23. A bearing 24 is mounted in the upper end of the cylinder and is provided at its upper end with an outstanding annular flange 25 seating upon the upper extremity of the cylinder and bolted thereto as at 26. 'The bearing 24 is provided intermediate its ends with a clearance space 21, for a purpose to be described. Aside from the space 21, the bearing 24 has a sliding fit with the interior of the cylinder 20, and the lower end of the bearing is grooved as at 28 to afford communication between the clearance space 21 and the cylinder 20 below the bearing. The bearing is provided with a suitable bushing 29 at the upper end of which is a packing ring 30 maintained in position by a plate 3|.

A plunger rod 32 reciprocates in the bushing 29 and is pivotally connected at its upper end as at 32' to the walking beam adjacent the well end thereof, as shown in Figure 1. The plunger rod 32 carries a plunger 33 at its lower end reciprocable in the cylinder 23 and occupying substantially the position shown in Figure 2 when the pump rods are at the lower limit of their down stroke. Under such conditions, it will be apparent that all fluid will be displaced from the lower end of the cylinder into the receiver upon each down stroke of the plunger.' The plunger is provided with a ring 34 above and below which are arranged packing cups 35 preferably having their flanges turned downwardly as shown in Figure 2. A clamping ring 36 retains the ring 34 and packing cups 35 in. position.

It will be apparent that reciprocation of the plunger 33 is utilized for compressing fluid in the receiver to store energy therein for use on each up stroke of the pump rods. Instead of using only air or some other compressible gas in the receiver, an important feature of the present invention is the provision of two bodies of fluid, one of which is compressible and the other of which is non-compressible. Accordingly the lower end of the receiver is provided with a body of a non-compressible fluid 31, preferably oil, and the space 33 above the body of oil is filled with a compressible 'fluid, preferably air. Upon each up stroke of the plunger oil will be drawn into the lower end of the cylinder 20 and upon each down stroke of the plunger, this element acts as a displacing member to displace oil from the cylinder into the receiver to raise the level thereof and thus compress the body of air. Inasmuch as the piston 33 has its lower extremity arranged below the lower extremity of the cylinder 23 when the piston reaches the lower end of its stroke, it will be apparent that any air which may have escaped past the packing rings 35 on the up stroke of the plunger will be discharged from the lower end of the cylinder and will find its way upwardly into the space 38. The quantity of oil in the receiver is such that when the plunger is at its upper limit of movement, the surface of the oil 31 will not be below the lower extremity of the cylinder 20. Thus it will be apparent that the oil, under all conditions, acts as a liquid seal between the plunger and the body of air, and this is highly important as will become apparent.

A reservoir 39 is employed as the source ofv oil for the receiver, and this reservoir preferably is part of a system which includes the connections for supplying oil to the receiver and connections for returning to the receiver any oil which escapes past the plunger. The reservoir is provided with a sight gauge 43. The reservoir is provided in the bottom thereof with an outlet pipe 4| communicating with the reservoir through an upstanding nipple 42 which tends to prevent any sediment in the oil from flowing into the pipe 4|. A stop cock 43 is provided in the pipe 4|, and a T 44 connects the pipe 4|, below the stop cock 43, to a pipe 45 leading to the intake side of an oil pump 46. The pump is provided with an outlet pipe 41. The oil pump 46 may be of any desired type and is convenient.- ly shown in Figure 2 as having a plunger 48 operated by a plunger rod 49. The pipes 45 and 41 are shown as being provided withcheck valves 5|] and 5| which, of course, may be embodied in the pump structure itself in accordance with conventional practice.

In Figure 1 the pump 46 has been shown as being connected to the reservoir 39 while the plunger rod 49 has been indicated as being pivotally connected as at 52 to one side of the receiver II. This pivotal connection is provided with a slight amount of play to permit the pin 52 to partake of slight vertical movement incidental to the swinging movement of the receiver about the pivot 15 during oscillating movement of the walking beam. The pump, of course, may be held stationary in any suitable manner, and the arrangement of the pump is such that the oil pump is operated through the medium of the horizontal component of movement of the pivot pin 52 during reciprocation of the plunger rod 32. It will become apparent that the very slight horizontal component of movement referred to is sufficient for maintaining any desired pressure within the receiver. It also will become apparent that even though the pump plunger partakes of a relatively short reciprocatory movement, an ample supply of oil for maintaining a varying pressure may be provided with a pump plunger and cylinder of small diameter. While the particular oil pumping means described is preferred, it is not essential to the operation of the broad features of the apparatus, and it will be apparent that the invention is not limited to any particular oil pumping means.

A T 53 is connected in the pipe 41 and leads to an adjustable blow-off valve indicated by the numeral 54 and having an outlet connected to a pipe 55. The valve 54 has not been specifically Figure 2, and the pipe 41 is provided with a pressure gauge 5'! between the blow-off valve 54 and the hose 56. Stop cocks 58 and 59 are preferably arranged on opposite sides of the pressure gauge 51, as shown.

The upper end of the cylinder 29 is provided with a lateral passage 68 to the outer end of which is connected a pipe 6!. The passage 60 communicates with the clearance space 21 near the bottom thereof, for a purpose to be described. A check valve 62 is connected to this pipe and opens outwardly to discharge oil from the clearance space 21 and a stop cook 63 is provided adjacent and outwardly of the check valve 62. The outer end of the pipe BI is connected by a flexible hose 64 to a pipe 65 leading to the top of the reservoir 39. The outlet pipe 55 of the blow-oil valve is connected to the pipe 65, and accordingly it will be apparent that oil discharged by the opening of the valve 54 will be returned to the reservoir.

It will be apparentthat the pump 46 is intended to generate pressure in the oil bein pumped at least as great as the maximum pressure present in the counterbalance unit during the normal operation thereof, and the counterbalance, pressure is determined by the setting Of the valve 54. Means are provided to permit the manual controlling of the pressure within the receiver in the event of failure of the valve 54 to function, such means also permitting oil to be blown under pressure from the receiver to the reservoir 39 if it is desired to empty the receiver for any reason. Stuch means forms no part of the present invention but is described and claimed in the copending application of I-Iarold W. Ramey, Serial No. 163,862, filed September 14, 1937. The means referred to comprises a pipe 66 provided with a manually operable control valve 61 and connected to the bottom of the receiver as shown in Figure 2. A stop cock 68 also is connected in the pipe 66, and this pipe is connected to the pipe 4|, as shown. Between the valve 61 and stop cook 68 a T 69 connects the pipe 66 to a valve 10 which may be opened together with the valve 61 if it is desired to drain the oil from the receiver without returning it to the reservoir.

As previously stated, the space 38 normally contains air or other compressible gas under pressure during the normal operation of the counterbalance unit, and reciprocation of the plunger 33 is utilized for charging the space 38. As shown in Figure 2, the upper end portion of the cylinder 20 is provided with a radial passage H, the inner end of which communicates with the clearance space 21 near the bottom thereof. A pipe 12 has one end connected to the outer endof the passage H and its other end connected to the pressure space 38 through the head I2. Two check valves 13 are connected in the pipe (I and open toward the pressure space 38. While one of the check valves 13 is sufficient, it is preferred that two be employed in order to insure against leakage of pressure from the space 38.

Between the passage H and check valves 13,.

a T 14 is connected in the pipe I2 and leads to an inwardly opening check valve 15 controlled by a valve 16 leading to the atmosphere and being manually controllable. When the valve 16 is open downward movement of the plunger 33 draws air into the upper end of the cylinder through the check valve 15, whereupon upward movement of the plunger 33 compresses the air of the cylinder to close the valve 15 and discharge the air into the space 38 through the check valves 13. Repeated reciprocation of the plunger 33, while the valve 16 is open, will charge the space 38 with air to the desired pressure, the valve 63 during such period, being closed.

As previously stated, reciprocation of the plunger 33 may be employed for charging the pressure space 38, and the rate of charging, of course, will depend upon the stroke of the plunger 33. For example, in a short stroke pumping rig the plunger 33 obviously will not reduce the volume of air in the cylinder 20 to as great an extent upon upward movement of the plunger as is true in a long stroke pumping unit. With a unitof the latter type, the plunger 33 moves upwardly practically to its limit of movement as defined by the lower end of the bearing 24. Under such conditions the air will be highly compressed and the receiver may be rapidly charged.

Much slower pumping will take place with a short stroke rig, and in fact, the maximum pressure generated in the cylinder 20 may not be sufficient to chargev the space 38 to the desired air pressure. Means are provided for reducing the effective clearance above the plunger 33 to provide an eliicient pumping action for charging the space 38 when the apparatus is used with a short stroke pumping unit, although such means, per se, forms no part of the present invention. A pipe 1'! is tapped into the pipe 66 between the valve 61 and the head I3, as shown in Figure 2. A manually controllable valve 18 is connected in the pipe 11 and above this valve is arranged an upwardly opening check valve 19. The upper end of the pipe 11 communicates with the pipe 6| between the check valve 62 and passage 60. As reciprocation of the plunger 33 takes place, pressure will increase within the receiver, and such pressure causes oil to be discharged through the pipe 11 into the upper end of the cylinder 20 when the valve 18 is open. The oil discharged into the cylinder 20 collects on the upper face of the plunger 33 to increase the effective length of this plunger and reduce the clearance space in the cylinder so that air may be compressed to a relatively high pressure to be discharged into the space 38.

As an alternative arrangement, a pipe 88 may be connected at one end to the pipe 11 and at its other end to the pipe 4'! between the blowoff valve 54 and the check valve 5!. A manually controllable valve 8| is arranged in the pipe 80. With the pump 46 in normal operation the valve 8| may be opened to permit oil to be pumped into the pipe H and thence into the upper end of the cylinder 28 to reduce the clearance space above the piston and thus provide for the effective compressing of the air to be discharged into the space 38.

As will become apparent, the combined use of compressible and non-compressible fluids provides a highly desirable degree of flexibility in the adjustment of the counterbalancing action which cannot be obtained with a purely pneumatic counterbalance. As will be described in detail later, the counterbalancing action is subject to variation in accordance with the relative volumes of the oil and air contained in the apparatus. The minimum quantity of oil in the apparatus is indicated by the level of the oil in Figure 2-, the minimum quantity of oil being such that when the plunger 33 is at the upper limit of its stroke, the level of the oil will not drop as far as the lower extremity of the cylinder 20. The quantity of the oil may be increased and the volume of the air above the oil decreased in order to vary the counterbalancing action. In order that increased flexibility of adjustment may be obtained, a valve 82 is adapted to release air from the air space 38 when it is desired to reduce the volume of the air and increase the volume of the oil without materially increasing the air pressure, as would occur if the volume of the oil were increased without releasing some of the air pressure from the space 38.

The characteristics of the system are such that the possibility of providing dangerous pressures within the receiver is negligible. In order to guard against any slight possibility of the bursting of the receiver due to excess pressures, it is desired to provide means for releasing the pressures when they accumulate above a predetermined point. This could be done, of course, by the provision of pressure relief valves, but since such valves normally would never operate, their use would not be satisfactory in view of the possibility of the corrosion and sticking of the valves. Accordingly it is desired to employ safety devices of the character shown in Figure 2 and indicated by the numeral 83.

Each of the devices 83 comprises a tubular member 84 having a cup shaped outer portion 85 having a frangible disk 86 therein retained in position by a threaded ring 81. One of the safety devices has its tubular member 84 communicating with the clearance space 21 while the other communicates directly with the air space 33 through the head l2. Upon the accumulation of pressures above the point of safety, the disks 86, or at least one of them, will be ruptured to release pressure from the chamber 38. These disks obviously are easily replaceable.

To facilitate the filling of the receiver with oil, the body of the receiver may be provided with a series of openings normally closed by threaded plugs 88 as shown in Figure 2. For most installations, the oil will be filled to the lowermost plug 88, which determines the level of the oil for the minimum quantity thereof whereby the level of the oil will never drop as low as the lower extremity of the cylinder 20.

A slightly modified form of counterbalance plunger is shown in Figure 3. It will be noted that in Figure 2, both of the cups 35 have their flanges turned downwardly. The form of the invention shown in Figure 3 is identical with the form previously described except that the upper cup 35 has its flange turned upwardly instead of downwardly, clamping ring '36 having its lower peripheral portion grooved to receive the flange of the upper cup 35.

The operation of the apparatus is as follows:

The upper end of the plunger rod 32 is connected to the walking beam as near as practicable to the well end of the beam, while the bottom of the receiver is pivoted to the foundation l1. Upon operation of the prime mover, power will be transmitted to the walking beam through the crank 5 and pitman 4, thus oscillating the walking beam in the usual manner. The oscillation of the pitman effects the reciprocation of the pump rods in the usual manner.

After the apparatus has been installed and it is desired to place it in operation, one of the plugs 88 is removed and oil is supplied to the receiver until the proper level of the oil is reached as determined from the opening from which the plug 88 has been removed. The oil charging operation is carried out with the walking beam at rest and with the well end of the beam in its lowermost position, the plunger 33 occupying the position shown in Figure 2.

After the receiver has been supplied with the proper volume of oil, the previously removed plug 88 is replaced. It will be apparent that the oil is supplied while atmospheric pressure is present in the receiver, and accordingly the oil need not be pumped against pressure when the receiver is charged. Having provided the desired amount of oil, the space 38 is then charged with air or other gas to the desired pressure, and the plunger 33 and cylinder 28 are adapted to be employed as the air pumping means.

In order to charge the receiver with air, it merely is necessary to open the valve 16 and start the prime mover in operation to oscillate the walking beam. During each downward movement of the plunger 33, air will be drawn into the upper portion of the cylinder 28 through the valve 16 and check valve I5. Upon each upward movement of the plunger 33, the check valve 15 will close and the air compressed in the cylinder 20 will be discharge-into the air space 38 through pipe 12 and check Valves 13.

It will be apparent that when the air charging operation is initiated atmospheric pressure is present in the space 38, and upward movement of the plunger a slight distance from its lower extremity of movement will compress the air in the cylinder 20 to a sufficient pressure to discharge the air into the receiver. As pressure accumulates in the receiver, it becomes necessary for the plunger '33 to move to progressively higher points in its up stroke before it will build up sufficient pressure in the cylinder 20 to .discharge the air into the receiver, it being necessary, of course, to compress the air in the cylinder 20 to a pressure above that in the space 38 before the air will be discharged into the receiver.

It will be apparent that the present apparatus is equally adapted for use with short stroke or long stroke pumping rigs. When employed with a long stroke rig, the plunger 38 moves upwardly upon each reciprocation to a point adjacent the lower end of the bearing '24, and accordingly air will be compressed in the cylinder to a sufficiently high pressure to charge the space 38to the desired pressure, for example, approximately 200 lbs. per square inch.

However, when the apparatus is employed with a short stroke pumping unit, the clearance space above the piston 33 will be of such volume as to prevent the building up of sufiicient pressure in the cylinder 20 to discharge air into the receiver upon each up stroke of the plunger. For this reason, means are provided for reducing the clearance space above the plunger 33 to assist in charging the receiver with air, although such means per se, forms no part of the present invention and is claimed in the copending application of Harold W. Ramey, referred to above.

In this connection it will be noted that during the air charging operation, the walking beam will be oscillated, and accordingly the pivot 32 (Figure 1) will swing about the axis of oscillation of the walking beam. The horizontal component of movement of the receiver I l is utilized for operating the oil pump. During the initial charging operation, the valve 58 may be closed to prevent the pumping of oil to the receiver during the air charging operation if the apparatus is being used with a long stroke pumping rig. With a short stroke rig, however, the valve 58 may be permitted to remain open to supply some additional oil to the receiver, and the valve 18 may be opened whereby the pressure accumulated within the receiver will discharge oil through the pipe 11 and passage 60 into the upper end of the cylinder 23. This oil will accumulate above the piston 33 to reduce the clearance space upon each up stroke of the plunger, thus permitting the building up of the necessary pressure to charge the receiver. In this connection it will be noted that the valve 18 may be opened prior to the opening of the valve 16, whereupon the partial vacuum created upon downward movement of the plunger 33 will create differential pressure between the upper end of the cylinder and the top of the receiver whereby atmospheric pressure will force oil through the pipe 11 into the top of the cylinder to reduce the clearance space above the plunger.

It will be obvious that the valve 18 will be closed after the desired quantity of oil has 001- lected above the plunger, whereupon continued operation of the plunger 33 charges the space 38 with the desired air pressure. As an alternative means for supplying oil to the cylinder 20 for the purpose stated, the Valve 8| may be opened to supply oil through the pipes and 11 to the cylinder to reduce the clearance space above the plunger 33. If the pipe 80 is to be used for this purpose, the valve 58 may be closed at least until the desired quantity of oil has collected above the plunger. e

The pressures within the receiver are readily determined from the gauge 51, and after the desired air pressure has been built up in the space 38, it is preferred that thewalking beam be stopped with the plunger 33 in its uppermost position and that the valve 16 be closed while the plunger is in such position. Under such con-v ditions, vacuum will be created in the cylinder 20 upon each downward stroke of the plunger 33, thus increasing the difierential pressures on opposite sides of the plunger 33 to provide a greater counterbalancing action for given pressures within the receiver. The feature of creating a partial vacuum above the plunger 33 forms no part of the present invention, but is claimed in the copending application of Harold W. Ramey, re-' ferred to above.

The apparatus is now ready for normal operation. During the rocking movement of the walking beam l, the plunger 33 will be reciprocated in the cylinder 20. During each downward movement of the plunger, this member displaces oil from the lower end of the cylinder 20 into the receiver thus raising the level ofthe oil in the receiver and compressing the air thereabove. Thus energy is stored by the compression of the of the plunger 33 to assist in lifting the well end of the walking beam. Thus the prime mover is relieved of the greater portion of the work required for each elevation of the pump rods.

The blow-off valve 54 is set for any desired op erating pressure and such pressure setting will determine the maximum pressure in the receiver. During any period of operation in which the pressure in the receiver drops below the pressure setting of the valve '54, oil will be pumped through pipe 41 and hose 58 into the receiver, and thus the pump 48 operates to maintain a predetermined maximum pressure within the receiver. The pump 46 operates continuously, and whenever the pressure in the receiver is above the predetermined maximum, the valve 54 opens to by-pass the oil through pipes 55 .and 65 to the reservoir 39.

It will be apparent that the present system takes care of any accumulation of oil above the plunger 33. As oil continues to accumulate above the plunger, it will reach the point where its level will be raised to the position of the passage 60 upon upward movement of the plunger 33. Oil cannot accumulate above such point since it will be discharged through the passage 60 upon upward movement of the plunger 33, and will pass through pipe '60, check valve 62, cut-off valve 33, hose 64 and pipe 65, and thence to the reservoir 39.

In view of the arcuate path of movement of the piston connection 32, it will be apparent that the oil pump plunger 49 will partake of two compression strokes for each complete oscillation of the walking beam. This fact, coupled with. the inherent characteristics of the apparatus wherein leakage of air pressure in the receiver is completely prevented, permits the retaining or increasing of the pressure in the receiver with the use of an extremely small oil pump.

If changes in pumping conditions render it desirable to increase or decrease the counterbalancing action, it merely is necessary to change the setting of the blow-off valve 54. If this valve is set for increased pressures, the oil pump will supply additional oil to the receiver to raise the" level of the oil and thus reduce the volume of the air while subjecting the air to increased pressures. If the valve 54 is set for a lower pressure, such pressure will be below the maximum pressure previously created within the receiver. Accordingly, the valve 54 will open as the plunger 53 approaches its limit of movement to discharge oil from the receiver back to the reservoir, through hose 55, pipe 57, valve 54, etc.

It will be apparent therefore that the valve 54 not only serves to determine the supplying of oil to the receiver from the pump, but that it also acts to release oil from the receiver to the reservoir. Thus the maximum pressure may be retained in the receiver in accordance with operating conditions. When the plunger 33 moves upwardly from its lowermost limit of movement, a drop in pressure occurs in the receiver, thus permitting the admission of oil into the receiver. Accordingly, downward movement of the plunger 33 will tend to build up the pressure above the predetermined maximum, andunder such conditions, the valve 54 will open to release the excess pressure. However, since oil is pumped at a very slow rate, only a very small amount of oil will be released from the receiver as the plunger 33 approaches its lower limit of movement. Accordingly, the maximum pressure is accurately maintained.

It also will be apparent that the valve 54 automatically compensates for variations in pressures in the receiver incident to temperature changes. For example, any lowering of pressures when the apparatus is operating at night or during cool weather will be prevented by the operation of the valve 54, any tendency for the maximum pressure to dropwithin the receiver being compensated for by an increased supply of oil to the receiver. Conversely, any tendency for the pressure to increase during warm periods of the day is prevented since the valve 54 functions in the manner stated to prevent any accumulation of pressure above the predetermined maximum. 7

As previouly stated, the present invention presents substantial advantages over purely pneumatic counterbalances, and particular attention is invited to one of such advantages through which a high degree of flexibility in the controlling of the counterb-alancing action is possible. In a purely pneumatic counterbalance, the variation between minimum and maximum pressures will always be determined by the relation between the piston displacement and the volume of the receiver. In other words, starting with a given minimum pressure, such a counterbalance will generate a predetermined maximum pressure in accordance with the relation between piston displacement and the volume of the system. This is not true of the present invention for the reason that the volume of the compressible fluid is variable independently of piston displacement.

Assuming that pumping conditions are such as to render desirable a limited differential between minimum and maximum pressures, such result is readily accomplished with the present apparatus by using the minimum quantity of oil, thus providing a maximum air volume in proportion to piston displacement. Thus minimum pressure changes will occur between minimum and maximum pressures, and such pressures may be determined by charging the air space 38 to the desired initial pressure.

Assuming that a greater differential between minimum and maximum pressures is desired, a higher oil level may be provided, thus reducing the volume of air in proportion to the piston displacement. Under such conditions the differential between minimum and maximum pressures may be increased. As a matter of fact, it is possible under such conditions to vary the pressures between atmospheric pressure as a minimum pressure and a very high pressure as a maximum pressure. Thus it will be apparent that the present system not only provides for the increasing or decreasing of minimum or maximum pressures but also provides for any desired differentials between such pressures. Such results are wholly impossible with a purely pneumatic counterbalance.

In connection with the foregoing advantages of the present system, attention is invited to the fact that if operating conditionsare such as to require a relatively great differential between' minimum and maximum pressures with a relatively low minimum pressure, the valve 82 may be opened to permit the escape of air toprovide av of the oil in the receiver and thus compress the air and store energy therein. The progressive increase in pressure as the plunger moves downwardly is important since the maximum pressure is reached at the point where it is necessary to overcome the maximum inertia or load prior to reversing its movement. Moreover, the maximum pressure is present at the point where it is necessary to overcome the great inertia of the load at the beginning of the upstroke of the pump rods.

As the plunger 33 moves upwardly,- tlie pres sure in the receiver causes the oil to be displaced therefrom to follow the plunger and exert a lifting force thereagainst. The greatest force is exerted at the bottom of the stroke and progressively decreases toward the top of the stroke. The flexibility of the system is such that any desired maximum pressure can be provided and this pressure can be progressively decreased to any desired minimum pressure, depending upon the characteristics of the particular installation. As stated above, the minimum and maximum pressures will not depend upon each other for the reason that the pressures in the receiver are variable and the relative volumes of the compressible and non-compressible fluids are variable. Accordingly, the counterbalancing characteristics of the apparatus may be accommodated to any installation.

For most installations, it is desirable that the average pressure within the receiver be such as to exert sumcient upward force on the well end of the walking beam to carry the weight of the pump rods plus one-half the weight of the liquid being pumped on each up stroke. Accordingly, the average load on the prime mover, both on the up and down strokes of the pump rods, will be equal to one-half the weight of the liquid being pumped on each up stroke of the pump rods. This fact, together with the fact that the pressures in the receiver vary from a maximum,

where the greatest load is to be carried, to a minimum, where the least load is to be carried, greatly smooths out the power demands on the prime mover.

From the foregoing description it will be obvious that the present apparatus possesses numerous distinct advantages over prior counterbalances, both of theweight and pneumatic types. For example, as distinguished from the use of counterweights on the walking beam, it will be apparent that the present apparatus permits the use of a relatively light beam, whereas materially heavier beams must be employed in order to carry the counterweights. Moreover, the present construction permits the .application of the counterbalancing force adjacent the well end of the beam, which is impossible with counter- Weighted crank structures. It also will be apparent that it is unnecessary totake into account the inertia of the weights of a weighted counterbalance, and the difilculties involved in shutting down the pumping rig to change the weights to alter the counterbalancing action are eliminated.

The present construction, weighing only a few thousand pounds, can be employed to provide any desired amount of counterbalancin effect from difi'erent minima to different maxima. When the present construction is employed for providing a maximum counterbalancing effect, it accomplishes the elimination of six to seven tons of counterweight. By eliminating the heavy mass of reciprocating or rotating counterweights, the pumping equipment is more po-rta ble, more easily installed, and requires very much less foundation for stability.

The apparatus also permits infinitely variable control of the counterbalancing effects within the limits of its capacity without involving the shutting down of the pumping rig. The apparatus further operates to reduce shock loads on all bearings and moving parts. The apparatus can be installed on any existing standard rig or conventional type of pumping unit, and attention is invited to the fact that the apparatus permits the elimination of the usual headache posts, since movement of the plunger 33 is limited in both directions to limit the swinging movement of the walking beam in either direction in the event of failure in the apparatus, such as the breakage of the pump rods or pitman.

The apparatus also possesses material advantages over purely pneumatic counterbalances. For example, all operating and sliding parts such as the valves, the oil pump, the counterbalance piston, etc., operate in oil and are sealed against oil instead of air, which prevents substantial difficulties. The same oil is always used, that portion which is not being actively used being stored in the reservoir.

Attention is invited to the fact that the same air is used, and this air does not come into contact with moving parts, and accordingly contamination from dust and corrosive gases is eliminated. The initial charge of air is confined in the receiver and sealed by oil so that all leakage of air is eliminated even over long shutdown periods.

The apparatus requires an oil pump of small capacity as distinguished from the use of a large capacity air pump or purely pneumatic counterbalances, and since the pump is pumping oil instead of air, there are no difliculties involved in the overheating of the pump. The use of the body of oil in the receiver eliminates contact between the air and the counterbalance, the work being transmitted from the plunger to the air only through the liquid medium. As a result, the present counterbalance is not as sensitive and quick acting as a straight pneumatic counterbalance, and accordingly impulse or shock loads are largely absorbed and cushioned by the inertia of the oil.

In addition to the general operation of the apparatus, attention is invited to some of the characteristics of the features of construction. For example, it will be noted that the clearance space 21 extends a substantial distance above the pas sages 60 and H. Accordingly, this clearance space, above the passages referred to, is always filled with air to prevent the generation of excess pressures above the plunger 33. This is particularly important when the space 38 is being charged with air upon the initial operation of the apparatus. The capacity of the clearance space 21 above the passages 60 and H may be designed to determine any maximum pressure which may be generated upon upward movement of the plunger 33. Accordingly, the clearance space '21 constitutes a safety featuresince it prevents the generation of any pressures which might be dangerous .to the apparatus upon upward movement of the plunger 33.

When the receiver is being charged with air by utilizing the plunger 33 as a pump plunger, this plunger moves upwardly from its lowermost position with atmospheric pressure present above the plunger and a greater pressure present below the plunger, depending upon the degree to which the receiver has been charged. During its upstroke, the plunger compresses the air in the cylinder 20 to a pressure equal to that in the receiver, whereupon further upward movement of the plunger increases the pressure of the air in the cylinder to discharge it into the receiver.

This condition is different from that found in any double acting pump since, in such a structure, the plunger does not compress a fluid at one side thereof .to be discharged into contact with the other side of the plunger. The conditions in the present construction permit the use of a different type of plunger packing as shown, for

example, in Figure 2. With this arrangement,

the flanges of the packing cups 35 are turned downwardly, and accordingly they provide positive sealing means during that portion of the upward movement of the plunger in which the pressure is greater below the plunger than above. Thus the escape of oil past the plunger is effectively prevented. After the plunger passes the point where pressures above and below it are equalized, it is necessary that the air above the plunger be compressed only sufficien-tly to overcome friction in the pipe connections 12 and check valves 13 in order that the air be discharged into the receiver.

Accordingly, it is unnecessary that the packing cups 35 seal against any great downward pressure. Ordinarily, these cups provide an efiective seal against the slight pressure above the plunger which is necessary to charge the receiver. However, any slight amount of air which passes down- 1 ceiver, regardless of what may happen accidentally to any of the piping tor valve connections. Upon the development of any pressure above the plunger materially greater than the pressure below the plunger, the cups would act to relieve the excess pressure above the plunger.

The packing arrangement referred to thus acts as an additional safety means, although there is substantially no danger whatever of breakage owing to the provision of the clearance space 21 and the frangible disks 86. Accordingly, if desired, the packing arrangement shown in Figure 3 may be provided, this arrangement forming an effective seal against leakage in both directions.

The receiver 39 has been shown in Figure 1 as being supported by the Sampson post. This is merely a convenient support, and it will be apparent that the reservoir, as well as the cylinder of the oil pump 46, may be supported by any suitable means.

A number of the valve connections in the system are provided as a matter of convenience. For example, the cut-01f valve 63 is open during normal operation of the apparatus but may be closed for servicing, and the same is true of the valves 59 and 61. The valve 10 may be opened together with the valve 61 if it is desired for any reason to drain the oil from the receiver without returning it to the reservoir.

The valve 61 may be opened while the valve HI remains closed if it is desired to utilize the pressure in the receiver for returning the oil from the receiver to the reservoir. Moreover, inthe event of failure of the blower-off valve 54 to function properly, an operator may control the valve 61 to by-pass oil from the receiver to the reservoir while watching the gauge 51 to control pressures in the receiver. The feature of by passing oil through the .pipe 66 under emergency conditions and the feature of utilizing vacuum in the upper end of the cylinder 20 for assisting in the counterbalancing action form no part of the pres ent invention, both of these features being described and claimed in the copending applicationof Harold W. Ramey, Serial No. 163,862, filed September 14, 1937. The feature of supplying oil through the pipe H or the pipe 80 to increase the effective length of the plunger 33 when charging the receiver with air, as for example when the apparatus is employed with a short stroke pumping rig, likewise forms, per se, no part of the present invention but is described and claimed in the copending application referred to.

While the two fluids in the receiver have been referred to as being air and oil, it will be apparent that these fluids are used as a matter of convenience and practicability. The invention obviously is not limited to the particular fluids employed but may use any suitable compressible and non-compressible fluids.

It is to be understood that the forms of the invention herewith shown anddescribed are to be taken as preferred examples of the same, and that various changes in the shape, size and "arrangement of parts may be made without departing from the spirit of the invention or the scope of the subj oined claims. 1

I claim:

1. A counterbalance for a member having uniform relative movement comprising a pair of structures one of which is connected to said member and the other of which is arranged below said member and connected to a stationary support, the second named structure having a cylinder and the first named structure having a plunger vertically reciprocable in said cylinder to displace fluid therefrom upon downward movement of said plunger, the counterbalance having a compression chamber into which fluid is displaced upon downward movement of said plunger, and a body of a non-compressible fluid in said second named structure trapping a body of a compressible fluid in said chamber, said non-compressible fluid being of a depth sufficient to trap compressible fluid in said chamber in any position of said plunger.

2. A counterbalance for a member having uniform relative movement comprising a pair of structures one of which is connected to said member and the other of which is arranged below said member and connected to a stationary support, the second named structure having a cylinder and the first named structure having a plunger vertically reciprocable in said cylinder to displace fluid therefrom upon downward movement of said plunger, one of said structures having a compression chamber into which fluid is displaced upon downward movement of said plunger, and a body of a non-compressible fluid in said second named structure trapping a body of a compressible fluid in said chamber, said non-compressible fluid being of a depth sufficient to trap compressible fluid in said chamber in any position of said plunger.

3. A counterbalance for parts having uniform relative movement comprising a vertical compression chamber, a vertical hollow member, an imperforate fluid displacing member vertically movable in said hollow member and projecting from the upper end thereof, the lower end of said ho-llow member being open for unrestricted communication with said compression chamber for the free passage of fluid back and forth between said chamber and the lower end of said hollow member, and a body of a non-compressible fluid trapping a body of a compressible fluid in the top of said compression chamber, said non-compressible fluid being of a depth sufficient to form a seal between said compressible fluid and said hollow member in any position of said displacing member.

4. A counterbalance comprising a compression chamber, a hollow member, a fluid displacing member movable in said hollow member, said compression chamber communicating with said hollow member to receive fluid displaced therefrom by said displacing member, a body of a noncompressible fluid trapping a body of a compressible fluid in the top of said compression chamber, said non-compressible fluid being of a depth suflicient to form a seal between said compressible fluid and said hollow member in any position of said displacing member, and means for introducing non-compressible fluid into said compression chamber against pressure therein.

5. A counterbalance comprising a compression chamber, a hollow member, a fluid displacing member movable in said hollow member, said compression chamber communicating with said hollow member to receive fluid displaced therefromby said displacing member, a body of a noncompressible fluid trapping a body of a compressible fluid in the top of said compression chamber, said non-compressible fluid being of a depth sufficient to form a seal between said compressible fluid and said hollow member in any position of said displacing member, means for supplying compressible fluid to said compression chamber to build up a pressure therein, and

means for introducing non-compressible fluid into said compression chamber against pressure therein.

6. A counterbalance comprising a compression chamber, a hollow member, a fluid displacing member movable in said hollow member, said compression chamber communicating with said hollow member to receive fluid displaced therefrom by said displacing member, a body of a noncompressible fluid trapping a body of a compressible fluid in the top of said compression chamber, said non-compressible fluid being of a depth sufiicient to form a seal between said compressible fluid and said hollow member in any position of said displacing member, pumping meansfor supplying non-compressible fluid to said compression chamber, and a blow off valve connected between said pumping means and said compression chamber.

7. A counterbalance comprising a compression chamber, a hollow member, a fluid displacing member movable in said hollow member, said compression chamber communicating with said hollow member to receive fluid displaced therefrom by said displacing member, a body of a noncompressible fluid trapping a body of a compressible fluid in the top of said compression chamber, said non-compressible fluid being of a depth sufficient to form a seal between said compressible fluid and said hollow member in any-position of said displacing member, pumping means for supplying non-compressible fluid to said compression chamber, a blow ofl valve connected between said pumping means and said compression chamber, a source of non-compressible fluid, and a by-pass connecting the outlet of said blow off valve to said source.

8. A counterbalance for parts having uniform relative movement comprising a compression chamber, a hollow vertical member, an imperioratefluid displacing member vertically movable in said hollow member, said compression chamber havingv unrestricted communication with the lower end of said hollow member to receive fluid displaced from said hollow member upon downward movement of said displacing member, and a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber, said non-compressible fluid being of a depth suflicient to form a seal between said compressible fluid and said hollow member in any vertical position of said displacing member.

9. A counterbalance comprising a compression chamber, a hollow vertical member, a fluid displacing member vertically movable in said hollow member, said compression chamber com-municating with the lower end of said hollow member to receive fluid displaced from said hollow member upon downward movement of said displacing member, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber, said non-compressible fluid being of a depth suflicient to form a seal between said compressible fluid and said hollow member in any vertical position of said displacing member, and means for supplying non-compressible fluid to said compression chamber.

10. A counterbalance comprising a compression chamber, a hollow vertical member, a fluid displacing member vertically movablein said hollow member, said compression chamber communicating with the lower end of said hollow member to receive fluid displaced from said hollow member upon downward movement ofsaid displacing member, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the topo-f said compression chamber, said non-compressible fluid being of a depth suflicient to form a seal between said compressible fluid and said hollow member in any vertical position of said displacing member, means for supplying compressible fluid to said compression chamber to build up a pressure therein, and means for supp-lying non-compressible fluid to said compression chamber against pressure there- 11. Acounterbalance,comprising a compression chamber, a hollow vertical member, a fluid. dise,

placing member vertically movable in said hollow member, said compression chamber communicating with the lower end of said hollow member to receive fluid displaced-from said hollow member'upon downwardmovement of said displacing member, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of'said compression chamber, said non-compressible fluid being of a depth suflicient to form a seal between said compressible fluid and said hollow member in any vertical position of said displacing member, a receptacle, pumping means for transferring noncompressible fluid under pressure from said re-- ceptacle to said compression chamber, a valve controlling communication between said pumping means and said compression chamber, and a by-pass from said valve to said receptacle.

12. A counterbalance comprising a compression chamber, a hollow vertical member, a fluid displacing member vertically movable in said hollow member, said compression chamber communicating with the lower end-of said hollow member to receive fluid displaced from said hollow member upon downward movement of said displacing member, a-body of a non-compressible fluid in said compression chamber trapping a body of 'a compressible fluid in the top of said compression chamber, said non-compressible fluid being'of a depth suificient to forma seal between said compressible fluid and'said hollow-member in any vertical position of said displacing member, pumping means'for supplying non-compressible fluid under pressure to said compression chamber, and

and said compression chamber.

13. A counterbalance comprising a compression chamber, a-hollow vertical member, a fluid displacing member vertically movable in said hollow member, said compression chamber communicating with the-lower end of said hollow member to receive fluid displaced from said hollow member upon downward movement of said displacing member, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the topof said compression chamber, said non-compressible fluid being of a depth suflicient to form a seal between said compressible-fluid and said hollow member in any vertical, position of said displacing member, pumping means for supplying non-compressible fluid under pressure to said compression chamber, a blow off valve between said pumping means and said compression chamber, a source of noncompressible fluid, and a by-pass connecting the outlet of said blow ofl valve to said source.

14. A counterbalance comprising a cylinder, a plunger reciprocable in said cylinder, a compressionchamber communicating with one end of said cylinder to receive fluid displaced therefrom upon movement of said piston toward said end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth suflicient to form a seal between said compressible fluid and said cylinder in any position of said plunger, a receptacle for said non-compressible fluid, and means for delivering fluid from said receptacle to said compression chamber during operation of said plunger.

15. A counterbalance comprising a cylinder, a plunger reciprocable in said cylinder, a compression chamber communicating with one end of said cylinder to receive fluid displaced therefrom upon movement of said piston toward said end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufficient to form a seal between said compressible fluid and said cylinder in any position of said plunger, a receptacle for said non-compressible fluid, means for delivering fluid from said receptacle tosaid compression chamber, and means for returning non-compressible fluid from the other end of said cylinder to said receptacle.

16. A counterbalance comprising a cylinder, a plunger reciprocable in said cylinder, a compression chamber communicating with one end of said cylinder to receive fluid displaced therefrom upon movement of said piston toward said end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth suflicient to form a seal between said compressible fluid and said cylinder in any position of said plunger,. a reservoir for, said non-compressible fluid, a pump for delivering fluid from said reservoir to said compression chamber, means between said pump and said compression chamber for determining the maximum pressure in said compression chamber, and a by-pass for non-compressible fluid connected between the other end of said cylinder and said reservoir.

17. A counterbalance comprising a cylinder, a plunger reciprocable in said cylinder, a compression chamber communicating with one, end of said cylinder to receive fluid displaced therefrom upon movement of said piston toward said end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth suflicient to form a seal between said compressible fluid and said cylinder in any position of said plunger, a reservoir for said non-compressible fluid, a pump for delivering fluid from said reservoir to said compression chamber, a blow off valve between said pump and said compression chamber, means for delivering non-compressible fluid from the outlet of said blow off valve to said reservoir, and means for returning non-compressible fluid from the other end of said cylinder to said reservoir.

18. A counterbalance comprising a cylinder, a plunger reciprocable in said cylinder, a compression chamber communicating with one end of said cylinder to receive fluid displaced therefrom upon movement of said piston toward said end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufficient to form a seal between said compressible fluid and said cylinder in any position of said plunger, a reservoir for said non-compressible fluid, a pump, an inlet pipe connected between said reservoir and said pump, an outlet pipe connected between said pump and said compression chamber to deliver non-compressible fluid from said pump to said compression chamber, a blow ofl valve connected in said outlet pipe to determine the maximum pressure in said compression chamber, a return pipe connected between the other end of said cylinder and said reservoir, and a by-pass connecting the outlet of said blow off valve to said return pipe.

19. A counterbalance comprising a cylinder, a plunger reciprocable in said cylinder, a compression chamber communicating with one end of said cylinder to receive fluid displaced from said cylinder upon movement of said plunger toward said end of said cylinder, means for supplying a compressible fluid to the other end of said cylinder including an inwardly opening check valve and a manually operable cut off Valve, and means connecting the second named end of said cylinder to said compression chamber and including a check valve opening inwardly with respect tosaid compression chamber.

20. A counterbalance comprising a vertical cylinder, a plunger reciprocable therein, a compression chamber communicating with the lower end of said cylinder to receive fluid displaced therefrom upon downward movement of said plunger, and abody of anon-compressible fluid in said com pression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufiicient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, said cylinder having a passage for non-compressible fluid communicating therewith above the upper limit of movement of said plunger, said cylinder having a clearance space above said passage.

21. A counterbalance comprising a vertical cyle inder, a plunger reciprocable therein, a compression chamber communicating with the lower end of said cylinder to receive fluid displaced therefrom upon downward movement of said plunger, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth suflicient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, an outlet communicating with the other end of said cylinder for the passage of non-compressible fluid accumulating to a predetermined depth above said plunger, said outlet having an outwardly opening check valve, and means for utilizing said plunger and the upper end of said cylinder for compressing a compressible fluid and transferring it to said compression chamber, said cylinder having a clearance space above said outlet.

an outlet communicating with the other end of said cylinder for the passage of non-compressible fluid accumulating to a predetermined depth above said plunger, said outlet having an outwardly opening check valve, said cylinder having a clearance space extending above said outlet, and means for utilizing said plunger and the upper end of said cylinder as a compression pump for charging said compression chamber with compressible fluid, comprising a check valve controlled connection between the upper end of said cylinder and said compression chamber.

23. A counterbalance for parts having uniform relative movement comprising a vertical cylinder, an imperforate piston vertically reciprocab-le in said cylinder, a compression chamber communicating with the lower end of said cylinder to receive fluid displaced therefrom upon downward movement of said plunger, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a minimum depth sufficient to form a seal between said compressible fluid and the lower end of said cylinder, said fluids being under pressure in said compression chamber, and means for varying the relative volumes of the compressible and noncompressible fluids to vary the counterbalancing action.

24. A counterbalance comprising a vertical cylinder, a piston vertically reciprocable in said cylinder, a compression chamber communicating with the lower end of said cylinder toreceive fluid displaced therefrom upon downward movement of said plunger, a body of a non-compressible fluid in said compression chamber trapping abody of a compressible fluid in the top of said compression chamber and being of a minimum depth suflicient to'form a seal between said compressible fluid and the lower end of said cylinder, said fluidsbeing under pressure in said compression chamber, means for supplying compressible fluid to and releasing it from said compression chamber, and means for supplying non-compressible fluid to and releasing it from said compression chamber,

said two means cooperating to maintain and control pressures in said compression chamber and to vary the relative volumes of said compressible and non-compressible fluids.

25. A counterbalance for parts having uniform relative movement, comprising a vertical cylinder, an imperforate piston vertically reciprocable. in said cylinder, a compression chamber surrounding said cylinder in fixed unrestricted Jcommunication with the lower end thereof, said compression chamber extending below said cylinder and being closed at its lower end, and a body of a non-compressible fluidin said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufllcient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said piston.

26. A counterbalance comprising a vertical cylinder, 2. piston vertically reciprocable in said cylinder, a compression chamber surrounding said cylinder and communicating with the lower end thereof, said compression chamber extending below said cylinder and being closed at its lower end, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufficient to form a sealbetween said compressible fluid and said cylinder in any vertical position of said piston,

and means for supplying non-compressible fluid; to said compression chamber against pressure therein.

27. A counterbalance comprising a vertical cylinder, a piston vertically reciprocable in said cylinder, a compression chamber surrounding said cylinder and communicating with the lower piston for charging said compression chamber with compressible fluid under pressure, and means for supplying non-compressible fluid to said compression chamber against pressure therein.

28. A counterbalance comprising a vertical cylinder, a piston vertically reciprocable in said cylinder, a compression chamber surrounding said cylinder and communicating with the lower end thereof, said compression chamber extending below said cylinder and being closed at its lower 7 I end, a body of a non-compressible fluid in saidcompression chamber trapping a body of a compressiblefluid in the top of said compression chamber and being of a depth sufficient to forma seal between said compressible fluid and said cylinder in any vertical position-0f said piston, means for utilizing upward movement of said plunger for charging said compression chamber with compressible fluid under pressure, a pump for supplying non-compressible fluid to said compression chamber, and an adjustable blow-Q off valve between said pump and said com pression chamber to determine the maximum pressure in said compression:chamber.

29. A counterbalance comprising a vertical cylinder, a piston vertically reciprocable in said cylinderya compression chamber surrounding 1 said cylinder and communicating with thelower end thereof, said compression chamber extending below said cylinder and being closed at its lower end, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible'fluid in the top of said compression chamber and being of a depth suflicient to form a seal between said compressible fluid" and said cylinder in any vertical position of said piston, means for utilizing upward movement ofsaid plunger for'charging said compression chamber with compressible fluid under pressure, a source of non-compressible fluid, a pump for transferring fluid from'said source to said compression chamber, and an adjustable blow-off valve between said pump. and said compression chamber for determining the maximum pressure in said compression chamber.

30. A counterbalance comprising a; vertical cylinder, a piston vertically reciprocable in said cylinder, a compression chamber surrounding said cylinder and communicating with the lower end thereof, said compression chamber extending below said cylinder and being closed at its lower end, a body of a non-compressible fluid in said piston, means for utilizing upward movement of said plunger for charging said compression chamber with compressible fluid under pressure, a source of non-compressible fluid, a pump for transferring fluid from said source to said compression chamber, an adjustable blowoff valve between said pump and said compression chamber for determining the maximum pressure at which non-compressible fluid will be supplied to said compression chamber, and a bypass connecting the outlet of said blow-off valve to said source.

31. The combination with a member mounte for movement through a fixed path, of a counterbalance comprising a pair of main relatively movable parts respectively connected to said member and to a stationary support, said relatively movable parts respectively comprising a substantially vertical cylinder and a substantially vertical plunger reciprocable therein, a compression chamber communicating with the lower end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufficient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, and means for varying the relative volumes of said fluids to vary the changes in pressure in said compression chamber between minimum and maximum pressures.

32. The combination with a member mounted for movement through a flxed path, of a counterbalance comprising a pair of main relatively movable parts respectively connected to said member and to a stationary support, said relatively movable parts respectively comprising a substantially vertical cylinder and a substantially vertical plunger reciprocable therein, a compression chamber communicating with the lower end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and. being of a depth sufiicient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, a receptacle for non-compressible fluid, means for supplying non-compressible fluid from said receptacle to said compression chamber, and means for varying the relative volumes of said fluids to vary the changes in pressure in said compression chamber between minimum and maximum pressures. v

33. The combination with a member mounted for movement through a fixed path, of a counterbalance comprising a pair of main relatively movable parts respectively connected to said member and to a stationary support, said relatively movable parts respectively comprising a substantially vertical cylinder and a substantially vertical plunger reciprocable therein, a compression chamber communicating with the lower end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufficient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, and constantly operating means tending to supply non-compressible fluid to said compression chamber.

34. The combination with a member mounted for movement through a fixed path, of a counterbalance comprising a pair of main relatively movable parts respectively pivotally connected to said member and to a stationary support, said relatively movable parts respectively comprising a substantially vertical cylinder and a substantially vertical plunger reciprocable therein, a compression chamber communicating with the lower end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufllcient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, and mechanism for supplying non-compressible fluid to said compression chamber.

35. The combination with a member mounted for oscillation about a horizontal axis, of a counterbalance comprising a pair of main relatively movable parts respectively pivotally connected to said oscillating member and to a stationary support, said relatively movable parts respectively comprising a substantially vertical cylinder and a substantially vertical plunger reciprocable therein, a compression chamber. communicating with the lower end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth suficient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, and means for utilizing the horizontal component of movement of the counterbalance for supplying non-compressible fluid to said compression chamber.

36. In combination with a walking beam pivoted for uniform oscillating movement about a horizontal axis, a counterbalance comprising a pair of structures one of which is pivotally connected to the walking beam and depends therefrom and the other of which is arranged below said walking beam and is pivotally connected to a vertical support, the second named structure having a cylinder and the first named structure having a plunger vertically reciprocable in said cylinder to displace fluid therefrom upon downward movement of said plunger, the counterbalance having a compression chamber into which fluid is displaced upon downward movement of said plunger, and a body of a non-compressible fluid in said second named structure trapping a body of a compressible fluid in said chamber, said non-compressible fluid being of a depth suflicient to trap compressible fluid in said structures having a compression chamber into which fluid is displaced upon downward movement of said plunger, and a body of a non-compressible fluid in said second named structure trapping a body of a compressible fluid in said chamber, said non-compressible fluid being of a depth sufficient to trap compressible fluid in said chamber in any position of said plunger.

38. The combination with a member mounted for movement through a fixed path, of a counterbalance comprising a pair of main relatively movable parts respectively connected to said member and to a stationary support, said relatively movable parts respectively comprising a substantially vertical cylinder and a substantially vertical plunger reciprocable therein, a compression chamber communicating with the lower end of said cylinder, and a body of a noncompressible fluid in said-compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth suflicient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger.

39. The combination with a member mounted for movement through a fixed path, of a counterbalance comprising a pair of main relatively movable parts respectively connected to said member and to a stationary support, said relatively movable parts respectively comprising a substantially vertical cylinder and a substantially vertical plunger therein, a compression chamber communicating with the lower end of said cylinder, a body of a non compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufficient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, and means for supplying non-compressible fluid to said compression chamberagainst pressure therein.

40. In combination with a walking beam pivoted for uniform oscillating movement about a horizontal axis, a counterbalance comprising a pair of structures one of which is pivotally connected to the walking beam and depends therefrom and the other of which is arranged below said walking beam and is pivotally connected to a vertical support, the second named-structure having a cylinder and the first named structure having a plunger vertically reciprocable in said cylinder to displace fluid therefrom upon'downward movement of said plunger, the counterbalance having a compression chamber into which fluid is displaced upon downward movement of said plunger, a body of a non-compressible fluid in said second named structure trapping a body of a compressible fluid in said chamber, said noncompressible fluid being of a depth sufficient to trap compressible fluid in said chamber in any position of said plunger, a receptacle for non-compressible fluid, and means for utilizing the horizontal component of movement of the counterbalance for transferring non-compressible fluid from said receptacle to said compression chamber.

41. In combination with a walking beam pivoted for uniform oscillating movement about a horizontal axis, a counterbalance comprising a pair of structures one of which is pivotally connected to the walking beam and depends therefrom and the other of which is arranged below said Walking beam and is pivotally connected to a vertical support, the second named structure having a cylinder and the first named structure having a plunger vertically reciprocable in said cylinder to displace fluid therefrom upon downward movement of said plunger, one of said structures having a compression chamber into which fluid is displaced upon downward movement of said plunger, a body of a non-compressible fluid in said second named structure trapping a body of a compressible fluid in said chamber, said non-compressible fluid being of a depth suflicient to trap compressible fluid in said cham-, ber in any position of said plungena receptacle for non-compressible fluid, and means for utilizing the horizontal component of movement of the counterbalance for transferring non-compressible fluid from said receptacle to said compression chamber.

42. The combination with a member mounted for oscillation about a horizontal axis, of a counterbalance comprising a pair of main relatively movable parts respectively pivotally connected to said oscillating memberand to a stationary support, said relatively movable parts respectively comprising a substantially vertical cylinder and a substantially vertical therein, a compression chamber communicating with the lower end of said cylinder, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and. be ing of a depth. sufllcient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger,a source of non-compressible fluid, and a pump for transferring non-compressible fluid from said source to said compression chamber, said pump comprising relatively movable members one of which is stationary and the other of which is connected to be operated through the horizontal component of movement of the counterbalance during operation of said oscillating member.

43. The combination with a member mounted for oscillation about a horizontal axis, of a counterbalance comprising a pair of main relatively movable parts respectively pivotally connected to said oscillating member and to a stationary support, said relatively movable parts respectively comprising a substantially vertical cylinder and a substantially vertical plunger reciprocable therein, a compression chamber communicating with'the lower end of said cylinderfa body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber'and being of a depth suilicient to form a seal between said compressible fluid and'thelower .end of said cylinder in any position of said plunger, means for utilizing the horizontal component of movement of the counterbalance for supplying noncompressible fluid to said compression chamber, and means for utilizing movement of said" comprising a substantially verticallcylinder and a substantially vertical plunger reciprocable therein, a compression chamber communicating with the lower end of said cylinder, a-body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufficient to form a seal between saidcompressible fluid and the lower end of said cylinder in any position of'saidplunger, a source of non-compressible fluid, a'pump for transferplunger reciprocable non-compressible fluid to ring non-compressible fluid from said source to said compression chamber, said pump comprising relatively movable members one of which is stationary and the other of which is connected to be operated through the horizontal component of movement of the counterbalance during operation of said oscillating member, and means for utilizing movement of said plunger in one direction for charging said compression chamber with compressible fluid under pressure.

45. The combination with a member mounted for oscillation about a horizontal axis, of a counterbalance comprising a substantially vertical plunger connected at its upper end to said oscillating member, a substantially vertical cylinder in which said plunger is reciprocable, a compression chamber surrounding and fixed to said cylinder and having a closed end extending beneath said cylinder and connected toa stationary support, said compression chamber communicating with the lower end of said cylinder to receive fluid displaced from said cylinder upon downward movement of said plunger, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufiicient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, and means for utilizing the horizontal component of movement of the counterbalance for supplying said compression chamber.

46. The combination with a member mounted for oscillation about a horizontal axis, of a counterbalance comprising a substantially Vertical plunger connected at its upper end to said oscillating member, a substantially vertical cylinder in which said plunger is reciprocable, a compression chamber surrounding and fixed to said cylinder and having a closed end extending beneath said cylinder and connected to a stationary support, said compression chamber communicating with the lower end of said cylinder to receive fluid displaced from said cylinder upon downward movement of said plunger, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth suflicient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, and a pump for supplying non-compressible fluid to said compression chamber, said pump comprising a pair of relatively movable parts one of which is connected to a stationary support and the other of which is connected to be operated by the horizontal component of movement of the counterbalance.

4'7. The combination with a member mounted for oscillation about a horizontal axis, of a counterbalance comprising a substantially vertical plunger connected at its upper end to said oscillating member, a substantially vertical cylinder in which said plunger is reciprocable, a compression chamber surrounding and fixed to said cylinder and having a closed end extending beneath said cylinder and connected to a stationary support, said compression chamber communicating with the lower end of said cylinder to receive fluid displaced from said cylinder upon downward movement of said plunger, a body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth suflicient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said plunger, means for utilizing the horizontal component of movement of the counterbalance.

for supplying non-compressible fluid to said compression chamber, and means for utilizing upward movement of said plunger for charging said chamber with compressible fluid under pressure.

48. A counterbalancing device for use with the walking beam of a well pump, said device comprising a piston and rod pivotally connected to the walking beam, a cylinder therefor pivoted for oscillating movement, a cushioning tank associated with said cylinder and normally in constant communication with the compression end thereof, the lower end of said tank and the compression end of the cylinder being filled with an incompressible fluid, a supply source for said fluid, and means operating incident to the oscillating movement of the cylinder whereby a predetermined fluid pressure will be maintained within said tank and the cylinder at a pressure not less than a predetermined pressure by the introduction of fluid from the said supply source to the cylinder.

49. A counterbalancing device for use with the walking beam of a well pump, said device comprising a piston and rod pivotally connected to the walking beam, a cylinder therefor pivoted for oscillating movement, a cushioning tank associated with said cylinder and normally in constant communication with the compression end thereof, the lower end of said tank and the compression end of the cylinder being filled with an incompressible fluid, a supply source for said fluid, and means operating incident to the oscillating movement of the cylinder whereby a predetermined fluid pressure will be maintained within said tank and the cylinder at a pressure not less than a predetermined pressure by the introduction of fluid from the said supply source to the cylinder, and means for venting the fluid pressure to the atmosphere when it exceeds a predetermined maximum pressure.

50. A counterbalance for use with a member mounted'for oscillation about a horizontal axis comprising a piston reciprocable by said member, a cylinder in which said piston reciprocates and which is oscillatable upon reciprocation of said piston in said cylinder, a compression chamber communicating with the lower end of said cylinder, a body of non-compressible fluid in said compression chamber trapping a body of compressible fluid in the top of said compression chamber and being of a depth sufficient to form a seal between said compressible fluid and the lower end of said cylinder in any position of said piston, and means for introducing non-compressible fluid into said compression chamber, said last named means including a pump operating incident to the reciprocation of said piston in said oscillatable cylinder.

51. A counterbalance device adapted to be interposed between the base and the walking beam of a pumping mechanism and to have free pivotal movement in the plane of oscillation of the walking beam, said device comprising a cushioning tank within which a compressible and an incompressible fluid are entrapped, a balancing cylinder in constant communication with the tank in the zone of the tank containing incompressible fluid, a piston within said balancing cylinder connected with the walking beam, the

lower end of the balancing cylinder being pivotally fixed to a base, means incident to the :operation of the piston in said balancing cylinder for forcing compressible fluid into the tank, and means controlled by pressure in the cushioning tank for feeding incompressible fluid thereto.

52. A counterbalance for parts having uniform relative movement comprising a compression chamber, a hollow member, a fluid displacing member movable in said hollow member, said compression chamber communicating with said hollow member to receive fluid displaced therefrom by said displacing member, a body of a non-compressible fluid trapping a body of a compressible fluid in the top of said compression chamber, said non-compressible fluid being of a depth suflicient to form a seal between said compressible fluid and said hollow member in any position of said displacing member, means for utilizing movement of said displacing member for charging said compression chamber with compressible fluid under pressure, and means for supplying non-compressible fluid to said compression chamber.

53. A counterbalance comprising a vertical cylinder, a piston vertically reciprocable in said cylinder, a compression chamber surrounding said cylinder and communicating with the lower end thereof, said compression chamber extending below said cylinder and being closed at its lower end, a. body of a non-compressible fluid in said compression chamber trapping a body of a compressible fluid in the top of said compression chamber and being of a depth sufficient to form a seal between said compressible fluid and said cylinder in any vertical position of said piston, means for utilizing movement of said piston for charging said compression chamber with compressible fluid under pressure, and means for supplying non-compressible fluid to said compression chamber against pressure therein.

54. In a power driven walking beam pump,

tion of the cushioning tank and the portion of i the balancing cylinder below its piston being filled with an incompressible fluid, the upper portion of the cushioning tank containing a compressible fluid, and separate means in communication with the cushioning tank whereby liquid may be automatically pumped into the tank when the fluid pressure in the tank drops below a predetermined value.

55. In a power driven walking beam pump, cushioning and counterbalancing means including a balancing cylinder pivoted to a base, a piston therein, a piston rod attached thereto and pivoted to the walking beam whereby oscillation of the walking beam will produce reciprocation of the piston, a cushioning tank, the lower end of which is in free communication with'the lower end of the balancing cylinder, said lower portion of the cushioning tank and the portion of the balancing cylinder below its piston being filled with an incompressible fluid, the upper porsure in the tank drops :below a predetermined 1' value, and means for automatically introducing additional quantities of incompressible fluid into the tank when the fluid pressure Within the tank is lowered to a predetermined value.

ROBERT GRIFFIN DE LA MATER. 

